Gas turbine engines are known to include a compressor wherein air is compressed to be then fed into a combustion chamber. Within the combustion chamber a fuel is injected into the compressed air and is combusted, generating high temperature and pressure flue gases that are expanded in a turbine.
A known gas turbine engine has a rotor shaft that carries at one end a compressor drum (carrying compressor rotor blades), and at the opposite end, turbine disks (carrying turbine rotor blades). The combustion chamber is provided between the compressor drum and the turbine disks.
The compressor drum has circumferential seats (shaped like circumferential dove tale slots) into which the compressor rotor blades are housed.
A casing is provided, which carries guide vanes for the compressor (compressor guide vanes) and for the turbine (turbine guide vanes).
The last stages of the compressor (where the air pressure is higher) can be thermally highly stressed.
The temperature of the compressed air at the outlet of the compressor can be high and the components at the last stages of the compressor can be cooled via cooling air injected into a gap between the compressor drum and the combustion chamber. The cooling air can be compressed air extracted downstream of the compressor before it enters the combustion chamber.
Therefore an equilibrium exists, which can allow a high lifetime for the parts concerned for the expected operating temperatures and stress, in particular, the compressor rotor, disk and blades that are the most stressed components of the compressor.
In order to increase power output and efficiency, it is desirable to increase the air mass flow through the compressor in order to increase the fuel mass flow that can be injected into the combustion chamber. This can increase the mass flow and temperature of the flue gases through the turbine.
Increasing the mass flow through the compressor can cause the temperature of the compressed air, for example, at the outlet of the compressor, to increase.
Such a temperature increase (tests showed that it could be as large as 20-30° C.) can influence the lifetime of the components affected.
With reference to FIG. 10 (curve A), the dependence of the lifetime of the parts, for example, the compressor, rotor, disk and blades, from the temperature of the compressed air at the compressor outlet is shown. From this diagram it is clear that also a small temperature increase (e.g., an increase of about 20-30° C.) can cause a large lifetime decrease. Such a lifetime decrease may not be acceptable, because it can cause the expected lifetime of the affected components to fall below the minimum admissible lifetime.